1. Field of the Invention
This invention relates to a corrosion testing method used in evaluating the corroded state of silver or silver alloys used in an electronic equipment for accelerated reproduction of the corrosion of the silver or silver alloys.
2. Description of the Related Art
Up to now, contact parts, such as switches or potentiometers, are routinely formed of silver or silver alloys as a contact material. These materials are hereinafter referred to as a silver-based contact part. On prolonged use by customers, these silver-based contact parts tend to undergo the corrosion of silver to give rise to contact troubles.
It is therefore necessary to evaluate long-term reliability of the silver-based contact parts and hence a variety of corrosion testing methods are presently used. Recently, in these corrosion tests, a gas mixture composed of plural gases is preferentially used for improving the reproducibility.
A number of testing methods have been reported by business concerns and research organizations, and a number of researches have been conducted. Specifically, these corrosion tests are conducted by setting up the atmosphere in which a silver-based contact part, if allowed to stand therein, is to undergo the state of corrosion, and by actually allowing the silver-based contact parts to stand therein.
With these testing methods, it is extremely difficult to set up a condition conforming to the targeted environment because the gas mixture is usually composed of three or more gas components. Moreover, although it is confirmed by these testing methods that the metals such as silver tends to undergo the corrosion, sufficient investigations into the correlation between the corrosion speed in the test environment and that in the actual operating environment have not been conducted to date.
Thus, in the conventional testing method, it has not been possible to reproduce and individually evaluate the advancing degree of the corrosion in the actual operating environment, even though relative corrosion evaluation can be achieved on plural different samples.
Therefore, in the conventional testing method, it has been necessary to approximate the testing condition to the actual using condition for evaluating the corrosion advancing degree in the actual using environment. Specifically, the conventional testing methods were conducted under a low concentration of the gas mixture as low as the ppb order, which accounts for the difficulty met in setting the aforementioned testing conditions.
Moreover, in the conventional testing methods, in which the gas mixture concentration is set to a lower value, the protracted testing time as long as two to three months is required for evaluating the long-term durability. This accounted for poor efficiency of the conventional testing method and difficulty met in achieving accurate evaluation.
Among the above-mentioned corrosion testing methods, a testing method prescribed in the standard for International Electrotechnical Commission (IEC) is in widespread use as a testing method for reproducing the corrosion of the metallic materials used as the contact materials for the electrical equipments. However, this IEC standard similarly suffers from the above-mentioned various drawbacks because the gas mixture is usually employed at a concentration of the order of ppbs.